Michael Jackson's death on Thursday caused a spike in visits to news Web sites that affected the performance and availability of some of the biggest ones, according to Web monitoring company Keynote Systems.

Between 6 p.m. and 8 p.m. U.S. Eastern Time, the availability for the news sites from ABC, CBS, and the L.A. Times dropped to almost 10 percent, meaning that about nine out of 10 visitors couldn't get the sites to load.

Starting at 5:30 p.m., the average download speed for news sites tracked by Keynote went from less than four seconds to almost 9 seconds, and their average availability dropped from almost 100 percent to 86 percent, the company said. News sites monitored by Keynote returned to normal performance and availability levels by 9:15 p.m.

Other news sites that experienced problems included AOL, MSNBC, NBC, the San Francisco Chronicle and Yahoo News, according to Keynote.

Meanwhile, Reuters' home page had a period of "significant slowdown" between around 6 p.m. to 7 p.m., according to Web monitoring company Pingdom.

Another high-profile news site that malfunctioned on Thursday was Google News, which interpreted the sharp spike in Jackson-related search queries as an automated attack. "As a result, for about 25 minutes yesterday, when some people searched Google News they saw a 'We're sorry' page before finding the articles they were looking for," Google said in an official blog on Friday. In general, Google saw a "volcanic" spike in Jackson-related search queries on Thursday, when more than 50 of the top-100 searches were related to him, a Google spokeswoman said via e-mail.

Akamai's Net Usage Index for global news sites traffic surged at around 6 p.m. and hit a peak of 4.24 million visitors per minute at 6:26 p.m.

The usage spike also put a strain on online communication tools, like AOL's AIM instant messaging system, which went offline for about 40 minutes on Thursday.

"At AOL our AIM instant messaging service was undergoing a previously scheduled software update which should normally prove routine. It proved not to be. There was a significant increase in traffic due to [Michael Jackson's] news and AIM was down for approximately 40 minutes this afternoon," the company said in a statement.

Microblogging site Twitter disabled for several hours a search feature in its homepage, although the company didn't respond to a request for comment as to whether this was caused by a Jackson-related surge in usage.

At Yahoo, the article headlined "Michael Jackson rushed to hospital" got the most hits of any other story ever posted on the company's home page with 800,000 clicks within 10 minutes. "Also, the news area on our front page experienced five times the amount of traffic it normally receives," Yahoo said in an official blog.

Yahoo News broke its record of unique visitors with 16.4 million; the previous record was 15.1 million visitors U.S. election day last year. In Yahoo Music, 21,000 people left comments on a blog post about Jackson, while more than 4,000 images related to the music star have been posted on Flickr in the past day, the company said

Facebook, the world's most popular social-networking site, experienced an increase across its core actions, like the posting of messages, notes and links on member profiles, a spokeswoman said via e-mail.

"Status updates in particular saw an increase of more than 3x the amount than usual within an hour of the MJ news breaking and remained well above our usual numbers for several hours," the spokeswoman said.

Jackson died unexpectedly at age 50 from a heart attack in Los Angeles as he was reportedly getting ready to launch a comeback. One of the biggest stars in pop music history, on par with icons like Elvis Presley and the Beatles, Jackson saw his star fade in the 1990s. One of the most successful recording artists of the 1970s and 1980s, Jackson later became more well known for scandals including accusations of child molestation and controversies over his multiple facial plastic surgeries.

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